Not applicable
This invention relates generally to battery recharging, and more particularly to systems for rechargeable battery cells.
Lithium-ion batteries are preferred over other types of rechargeable batteries, such as nickel-cadmium batteries and nickel metal-hydride batteries, for portable electronics applications because of their light weight and high energy density. Lithium-ion batteries, however, are very sensitive to overcharging and safety is a concern with their use. For example, metallic lithium may plate onto an electrode within the battery cell should the battery cell become overcharged. The plated lithium can pose a fire hazard due to the flammable nature of metallic lithium. Another safety concern involves the venting of noxious fumes when the temperature of the battery cell becomes too high. Furthermore, an over-discharge condition can result in a change in the chemical composition of the electrolyte in the battery cell, which can significantly shorten the life of the battery cell.
A battery cell may also be irreparably damaged by water intrusion. In particular, the water can short circuit components of the circuit which are connected to the battery cell. The short circuit condition can result in a current surge from the battery cell, which can damage the circuit components and cause a catastrophic failure in the battery cell itself. Hence, it is important to have a battery protection system that accurately monitors battery cells and ensures that they operate within safe parameters.
The present invention relates to a protection circuit for use with a battery operated device. The protection circuit can be incorporated into a battery or battery pack, a battery charging device or the battery operated device. The battery operated device can be for example a radio, a cellular telephone, a cordless telephone, a cordless tool, a video recording device, an audio recording device, a camera, a cordless shaver, a cordless toothbrush or a toy.
The protection circuit can include an over temperature detector, a controller, and a voltage divider circuit. The voltage divider circuit can include at least a multi-use thermistor for monitoring a temperature of the battery cell (or cells), the battery charger, or the battery operated device. Upon the monitored temperature exceeding a predefined value, the over temperature detector can signal the controller to terminate the charging and/or discharging of the battery cell or cells. It should be understood within contemplation of the present invention that the xe2x80x9cpredefined valuexe2x80x9d for a voltage or a temperature can be understood as a predefined value range of voltages or temperature. It should also be understood that the present invention is applicable to both single cell and multi-cell batteries or battery packs, and the subsequent use of xe2x80x9cbatteryxe2x80x9d, xe2x80x9cbattery cellxe2x80x9d, or xe2x80x9cbattery packxe2x80x9d should be interpreted in this context. Further, a temperature monitor can be operatively connected to the thermistor to output a temperature value derived from a voltage applied across the thermistor. The voltage divider circuit also can include a resistor which can be disposed in the battery operated device.
The protection circuit also can include an overcharge detector and a first logic gate. The first logic gate, which can be an OR gate, can have an output operatively connected to the controller, a first input operatively connected to an output of the over temperature detector, and a second input operatively connected to an output of the overcharge detector. The first logic gate can signal the controller to terminate charging of the battery cell upon the occurrence of the first logic gate receiving a signal from the over temperature detector or the overcharge detector.
The protection circuit can further include a device discharge detector, wherein the device discharge detector signals the controller to terminate discharging of the battery cell if a voltage applied to the battery operated device from the battery cell is less than a predefined value. The device discharge detector also can terminate the discharging of the battery cell upon the occurrence of a specified condition, such as water intrusion into the battery operated device or battery cell pack, an internal circuit failure within the battery operated device, a software failure within the battery operated device, or a software failure external to the battery operated device.
An over discharge detector and a second logic gate, which can be an AND gate, can be included. The second logic gate can have an output operatively connected to the controller, a first input operatively connected to an output of the device discharge detector, and a second input operatively connected to an output of the over discharge detector. The second logic gate can signal the controller to terminate charging of the battery cell upon the second logic gate receiving a signal from the over temperature detector or the overcharge detector.
The present invention also can include a method of providing device protection for a battery operated device. The method can include the step of monitoring a voltage of at least one battery cell. Further, the temperature of the battery cell, a battery charger, or the battery operated device can be monitored using a thermistor. The thermistor can be used to monitor a voltage applied to, or supplied from, a battery protection circuit. The charge and/or discharge of the battery cell can be terminated upon the monitored temperature exceeding a predefined value. The method also can include the steps of terminating the charge and/or discharge of the battery cell upon a voltage applied to, or supplied from, a battery protection circuit being too high or too low. The charge and/or discharge also can be terminated if the voltage measured at the battery cell is too high or too low.